Neural basis for sentence comprehension deficits in frontotemporal dementia

Many patients with frontotemporal dementia (FTD) have impaired sentence comprehension. However, the pattern of comprehension difficulty appears to vary depending on the clinical subgroup. The purpose of this study was to elucidate the neural basis for these deficits in FTD. We studied patients with two different presentations: Three patients with Progressive Non-Fluent Ahasia (PNFA), and five non-aphasic patients with a dysexecutive and social impairment (EXEC). The FTD patient subgroups were compared to a cohort of 11 healthy seniors with intact sentence comprehension. We monitored regional cerebral activity with blood oxygen level dependent (BOLD) functional magnetic resonance imaging (fMRI) while subjects read sentences featuring both a grammatically complex object-relative center-embedded clause and a long linkage between the head noun phrase (NP) and the gap where the NP is interpreted in the center-embedded clause. Subjects decided whether the agent of the action is a male or a female. Healthy seniors activated both ventral portions of inferior frontal cortex (vIFC) and dorsal portions of IFC (dIFC) in the left hemisphere, often associated with grammatical and working memory components of these sentences, respectively. PNFA patients differed from healthy controls since they have reduced activation of left vIFC, while EXEC patients have less recruitment of left dIFC. We conclude that FTD subgroups have distinct patterns of sentence comprehension difficulty in part because of selective interruptions of a large-scale neural network for sentence processing.     

Brain activation during the course of sentence comprehension

The purpose of this study is to determine, by functional magnetic resonance imaging, how the activated regions of the brain change as a Japanese sentence is presented in a grammatically correct order. In this study, we presented constituents of a sentence to Japanese participants one by one at regular intervals. The results showed that the left lingual gyrus was significantly activated at the beginning of the sentence, then the left inferior frontal gyrus and left supplementary motor area, in the middle of the sentence, and the left inferior temporal gyrus, at the end of the sentence. We suggest that these brain areas are involved in sentence comprehension in this temporal order.     

Large-scale neural network for sentence processing

Our model of sentence comprehension includes at least grammatical processes important for structure-building, and executive resources such as working memory that support these grammatical processes. We hypothesized that a core network of brain regions supports grammatical processes, and that additional brain regions are activated depending on the working memory demands associated with processing a particular grammatical feature. We used functional magnetic resonance imaging (fMRI) to test this hypothesis by comparing cortical activation patterns during coherence judgments of sentences with three different syntactic features. We found activation of the ventral portion of left inferior frontal cortex during judgments of violations of each grammatical feature. Increased recruitment of the dorsal portion of left inferior frontal cortex was seen during judgments of violations of specific grammatical features that appear to involve a more prominent working memory component. Left posterolateral temporal cortex and anterior cingulate were also implicated in judging some of the grammatical features. Our observations are consistent with a large-scale neural network for sentence processing that includes a core set of regions for detecting and repairing several different kinds of grammatical features, and additional regions that appear to participate depending on the working memory demands associated with processing a particular grammatical feature.     

Dissociable patterns of brain activity during comprehension of rapid and syntactically complex speech: evidence from fMRI

Sentence comprehension is a complex task that involves both language-specific processing components and general cognitive resources. Comprehension can be made more difficult by increasing the syntactic complexity or the presentation rate of a sentence, but it is unclear whether the same neural mechanism underlies both of these effects. In the current study, we used event-related functional magnetic resonance imaging (fMRI) to monitor neural activity while participants heard sentences containing a subject-relative or object-relative center-embedded clause presented at three different speech rates. Syntactically complex object-relative sentences activated left inferior frontal cortex across presentation rates, whereas sentences presented at a rapid rate recruited frontal brain regions such as anterior cingulate and premotor cortex, regardless of syntactic complexity. These results suggest that dissociable components of a large-scale neural network support the processing of syntactic complexity and speech presented at a rapid rate during auditory sentence processing.     

Brain activity varies with modulation of dynamic pitch variance in sentence melody

Fourteen native speakers of German heard normal sentences, sentences which were either lacking dynamic pitch variation (flattened speech), or comprised of intonation contour exclusively (degraded speech). Participants were to listen carefully to the sentences and to perform a rehearsal task. Passive listening to flattened speech compared to normal speech produced strong brain responses in right cortical areas, particularly in the posterior superior temporal gyrus (pSTG). Passive listening to degraded speech compared to either normal or flattened speech particularly involved fronto-opercular and subcortical (Putamen, Caudate Nucleus) regions bilaterally. Additionally the Rolandic operculum (premotor cortex) in the right hemisphere subserved processing of neat sentence intonation. As a function of explicit rehearsing sentence intonation we found several activation foci in the left inferior frontal gyrus (Broca's area), the left inferior precentral sulcus, and the left Rolandic fissure. The data allow several suggestions: First, both flattened and degraded speech evoked differential brain responses in the pSTG, particularly in the planum temporale (PT) bilaterally indicating that this region mediates integration of slowly and rapidly changing acoustic cues during comprehension of spoken language. Second, the bilateral circuit active whilst participants receive degraded speech reflects general effort allocation. Third, the differential finding for passive perception and explicit rehearsal of intonation contour suggests a right fronto-lateral network for processing and a left fronto-lateral network for producing prosodic information. Finally, it appears that brain areas which subserve speech (frontal operculum) and premotor functions (Rolandic operculum) coincidently support the processing of intonation contour in spoken sentence comprehension.     

Deriving meaning: Distinct neural mechanisms for metaphoric, literal, and non-meaningful sentences

In this study, we used a novel cognitive paradigm and event-related functional magnetic resonance imaging (ER-fMRI) to investigate the neural substrates involved in processing three different types of sentences. Participants read either metaphoric (Some surgeons are butchers), literal (Some surgeons are fathers), or non-meaningful sentences (Some surgeons are shelves) and had to decide whether they made sense or not. We demonstrate that processing of the different sentence types relied on distinct neural mechanisms. Activation of the left inferior frontal gyrus (LIFG), BA 47, was shared by both non-meaningful and metaphoric sentences but not by literal sentences. Furthermore, activation of the left thalamus appeared to be specifically involved in deriving meaning from metaphoric sentences despite lack of reaction times differences between literals and metaphors. We assign this to the ad hoc concept construction and open-endedness of metaphoric interpretation. In contrast to previous studies, our results do not support the view the right hemispheric is specifically involved in metaphor comprehension.     

Laterality in metaphor processing: lack of evidence from functional magnetic resonance imaging for the right hemisphere theory

We investigated processing of metaphoric sentences using event-related functional magnetic resonance imaging (fMRI). Seventeen healthy subjects (6 female, 11 male) read 60 novel short German sentence pairs with either metaphoric or literal meaning and performed two different tasks: judging the metaphoric content and judging whether the sentence has a positive or negative connotation. Laterality indices for 8 regions of interest were calculated: Inferior frontal gyrus (opercular part and triangular part), superior, middle, and inferior temporal gyrus, precuneus, temporal pole, and hippocampus. A left lateralised network was activated with no significant differences in laterality between the two tasks. The lowest degree of laterality was found in the temporal pole. Other factors than metaphoricity per se might trigger right hemisphere recruitment. Results are discussed in the context of lesion and hemifield studies.     

Experiential simulations of negated text information

We investigated the question of whether comprehenders mentally simulate a described situation even when this situation is explicitly negated in the sentence. In two experiments, participants read negative sentences such as There was no eagle in the sky, and subsequently responded to pictures of mentioned entities in the context of a recognition task. Participants' responses following negative sentences were faster when the depicted entity matched rather than mismatched the negated situation. These results suggest that comprehenders simulate the negated situation when processing a negated sentence. The results thereby provide further support for the experiential-simulations view of language comprehension.     

Experiential simulations of negated text information

We investigated the question of whether comprehenders mentally simulate a described situation even when this situation is explicitly negated in the sentence. In two experiments, participants read negative sentences such as There was no eagle in the sky, and subsequently responded to pictures of mentioned entities in the context of a recognition task. Participants' responses following negative sentences were faster when the depicted entity matched rather than mismatched the negated situation. These results suggest that comprehenders simulate the negated situation when processing a negated sentence. The results thereby provide further support for the experiential-simulations view of language comprehension.     

Concrete spatial language: see what I mean?

Conveying complex mental scenarios is at the heart of human language. Advances in cognitive linguistics suggest this is mediated by an ability to activate cognitive systems involved in non-linguistic processing of spatial information. In this fMRI-study, we compare sentences with a concrete spatial meaning to sentences with an abstract meaning. Using this contrast, we demonstrate that sentence meaning involving motion in a concrete topographical context, whether linked to animate or inanimate subjects nouns, yield more activation in a bilateral posterior network, including fusiform/parahippocampal, and retrosplenial regions, and the temporal-occipital-parietal junction. These areas have previously been shown to be involved in mental navigation and spatial memory tasks. Sentences with an abstract setting activate an extended largely left-lateralised network in the anterior temporal, and inferior and superior prefrontal cortices, previously found activated by comprehension of complex semantics such as narratives. These findings support a model of language, where the understanding of spatial semantic content emerges from the recruitment of brain regions involved in non-linguistic spatial processing.     

Neural correlates of metonymy resolution

Metonymies are exemplary models for complex semantic association processes at the sentence level. We investigated processing of metonymies using event-related functional magnetic resonance imaging (fMRI).During an 1.5 Tesla fMRI scan, 14 healthy subjects (12 female) read 124 short German sentences with either literal (like “Africa is arid”), metonymic (“Africa is hungry”), or nonsense (“Africa is woollen”) content. Sentences were constructed so that they obey certain grammatical, semantic, and plausibility conditions and were matched for word frequency, semantic association, length and syntactic structure. We concentrated on metonymies that were not yet fossilised; we also examined a wide variety of metonymic readings.Reading metonymies relative to literal sentences revealed signal changes in a predominantly left-lateralised fronto-temporal network with maxima in the left and right inferior frontal as well as left middle temporal gyri. Left inferior frontal activation may reflect both inference processes and access to world knowledge during metonymy resolution.     

文盲与非文盲汉字字形和语音加工的脑机制

利用功能性磁共振成像(fMRI)技术探讨文盲和非文盲汉字字形和语音加工脑机制的差异。实验1使用汉字字形和图形比较了中国人文盲和非文盲字形加工过程脑机制的左侧差异。实验2使用汉字语音和纯音比较了文盲和非文盲语音加工过程脑机制的双侧差异。结果表明文盲与非文盲汉字字形和语音加工脑机制不同,且非文盲的脑活动强。     

理解能力不同的个体抑制干扰信息的效率

根据多媒语言理解测试 ,筛选出汉语综合理解能力高、低不同的两组被试 ,采用固定速移动窗口阅读与选择性再认相结合的实验范式 ,在两个实验中考察了两组被试在理解加工汉语双字词和两从句复合句的过程中对外在干扰信息的抑制效率。词汇加工与句子加工两个实验的结果一致表明 :不同语言理解能力的个体在抑制干扰信息的效率上存在差异 ,低理解能力者的抑制效率也较低 ;抑制效率受到干扰材料意义性的影响 ,越有意义的干扰越难以被抑制     

Sentence processing in Lewy body spectrum disorder: the role of working memory

Prior work has related sentence processing to executive deficits in non-demented patients with Parkinson's disease (PD). We extended this investigation to patients with dementia with Lewy bodies (DLB) and PD dementia (PDD) by examining grammatical and working memory components of sentence processing in the full range of patients with Lewy body spectrum disorder (LBSD). Thirty-three patients with LBSD were given a two-alternative, forced-choice sentence-picture matching task. Sentence type, working memory, and grammatical structure were systematically manipulated in the sentences. We found that patients with PDD and DLB were significantly impaired relative to non-demented PD patients and healthy controls. The deficit in PDD/DLB was most pronounced for sentences lengthened by the strategic placement of an additional prepositional phrase and for sentences with an additional proposition due to a center-embedded clause. However, there was no effect for subject-relative versus object-relative grammatical structure. An MRI voxel-based morphometry analysis in a subset of patients showed significant gray matter thinning in the frontal lobe bilaterally, and this extended to temporal, parietal and occipital regions. A regression analysis related sentence processing difficulty in LBSD to frontal neocortex, including inferior prefrontal, premotor, and dorsolateral prefrontal regions, as well as right superior temporal cortex. These findings are consistent with the hypothesis that patients with PDD and DLB have difficulty processing sentences with increased working memory demands and that this deficit is related in part to their frontal disease.     

Prominence vs. aboutness in sequencing: A functional distinction within the left inferior frontal gyrus

Prior research on the neural bases of syntactic comprehension suggests that activation in the left inferior frontal gyrus (lIFG) correlates with the processing of word order variations. However, there are inconsistencies with respect to the specific subregion within the IFG that is implicated by these findings: the pars opercularis or the pars triangularis. Here, we examined the hypothesis that the dissociation between pars opercularis and pars triangularis activation may reflect functional differences between clause-medial and clause-initial word order permutations, respectively. To this end, we directly compared clause-medial and clause-initial object-before-subject orders in German in a within-participants, event-related fMRI design. Our results showed increased activation for object-initial sentences in a bilateral network of frontal, temporal and subcortical regions. Within the lIFG, posterior and inferior subregions showed only a main effect of word order, whereas more anterior and superior subregions showed effects of word order and sentence type, with higher activation for sentences with an argument in the clause-initial position. These findings are interpreted as evidence for a functional gradation of sequence processing within the left IFG: posterior subportions correlate with argument prominence-based (local) aspects of sequencing, while anterior subportions correlate with aboutness-based aspects of sequencing, which are crucial in linking the current sentence to the wider discourse. This proposal appears compatible with more general hypotheses about information processing gradients in prefrontal cortex (Koechlin & Summerfield, 2007).     

Functional MRI of conventional and anomalous metaphors in Mandarin Chinese

This study looks at whether conventional and anomalous metaphors are processed in different locations in the brain while being read when compared with a literal condition in Mandarin Chinese. We find that conventional metaphors differ from the literal condition with a slight amount of increased activation in the right inferior temporal gyrus. In addition, when the anomalous metaphor condition is compared with the literal condition, increased activation occurs bilaterally in the frontal and temporal gyri. Lastly, the comparison between the anomalous and conventional metaphor conditions shows bilateral activation in the middle frontal gyrus and the precentral gyrus, and right-hemisphere activation in the superior frontal gyrus. Left hemisphere activation is found in the inferior frontal gyrus and fusiform gyrus. The left hemisphere activation in the frontal and temporal gyri point to the recruitment of traditional language-based areas for anomalous metaphor sentences, while the right-hemisphere activation found suggests that remote associations are being formed. In short, our study supports the idea that metaphors are not a homogenous type of figurative language and that distinguishing between different types of metaphors will advance theories of language comprehension.     

Enhanced left frontal involvement during novel metaphor comprehension in schizophrenia: Evidence from functional neuroimaging

The neural basis involved in novel metaphor comprehension in schizophrenia is relatively unknown. Fourteen people with schizophrenia and fourteen controls were scanned while they silently read novel metaphors, conventional metaphors, literal expressions, and meaningless word-pairs. People with schizophrenia showed reduced comprehension of both novel and conventional metaphors. Furthermore, while controls showed enhanced brain activation in right inferior frontal gyrus (IFG) for novel metaphors versus meaningless word-pairs, people with schizophrenia showed an over-activation of left IFG and middle frontal gyrus (MFG). Direct comparison between the groups revealed greater activation in left precuneus for both novel metaphors and literal expressions vs. baseline for individuals with schizophrenia. Direct comparison for novel metaphors vs. literal expressions also revealed increased activation for individuals with schizophrenia in left MFG. These results suggest that the inefficient processing of novel metaphors in schizophrenia involves compensatory recruitment of additional brain regions that include the left MFG and left precuneus.     

Differences in semantic encoding as a function of reading comprehension skill

Using a modified Stroop procedure, we examined the extent to which the semantic encoding of a word is governed by the context within which that word appears. Good and poor comprehenders named the color of target words following their reading of either sentences or single words representing the object nouns of the sentences. Target words represented contextually emphasized (appropriate) attributes of the object nouns, nonemphasized (inappropriate) attributes of these nouns, or object attributes not related to these nouns (neutral). For single-word contexts, all subjects exhibited equal semantic interference to appropriate and inappropriate targets, relative to neutral targets. For sentence contexts, however, good comprehenders exhibited semantic interference only to appropriate targets, whereas poor comprehenders again exhibited equal interference to appropriate and inappropriate targets. These findings suggest that differences in comprehension skill may be attributable, at least in part, to fundamental differences in the way in which sentences are semantically encoded.     

What artificial grammar learning reveals about the neurobiology of syntax

In this paper we examine the neurobiological correlates of syntax, the processing of structured sequences, by comparing FMRI results on artificial and natural language syntax. We discuss these and similar findings in the context of formal language and computability theory. We used a simple right-linear unification grammar in an implicit artificial grammar learning paradigm in 32 healthy Dutch university students (natural language FMRI data were already acquired for these participants). We predicted that artificial syntax processing would engage the left inferior frontal region (BA 44/45) and that this activation would overlap with syntax-related variability observed in the natural language experiment. The main findings of this study show that the left inferior frontal region centered on BA 44/45 is active during artificial syntax processing of well-formed (grammatical) sequence independent of local subsequence familiarity. The same region is engaged to a greater extent when a syntactic violation is present and structural unification becomes difficult or impossible. The effects related to artificial syntax in the left inferior frontal region (BA 44/45) were essentially identical when we masked these with activity related to natural syntax in the same subjects. Finally, the medial temporal lobe was deactivated during this operation, consistent with the view that implicit processing does not rely on declarative memory mechanisms that engage the medial temporal lobe. In the context of recent FMRI findings, we raise the question whether Broca’s region (or subregions) is specifically related to syntactic movement operations or the processing of hierarchically nested non-adjacent dependencies in the discussion section. We conclude that this is not the case. Instead, we argue that the left inferior frontal region is a generic on-line sequence processor that unifies information from various sources in an incremental and recursive manner, independent of whether there are any processing requirements related to syntactic movement or hierarchically nested structures. In addition, we argue that the Chomsky hierarchy is not directly relevant for neurobiological systems.     

An event-related fMRI study of syntactic and semantic violations

We used event-related functional magnetic resonance imaging to identify brain regions involved in syntactic and semantic processing. Healthy adult males read well-formed sentences randomly intermixed with sentences which either contained violations of syntactic structure or were semantically implausible. Reading anomalous sentences, as compared to well-formed sentences, yielded distinct patterns of activation for the two violation types. Syntactic violations elicited significantly greater activation than semantic violations primarily in superior frontal cortex. Semantically incongruent sentences elicited greater activation than syntactic violations in the left hippocampal and parahippocampal gyri, the angular gyri bilaterally, the right middle temporal gyrus, and the left inferior frontal sulcus. These results demonstrate that syntactic and semantic processing result in nonidentical patterns of activation, including greater frontal engagement during syntactic processing and larger increases in temporal and temporo-parietal regions during semantic analyses.